Biotheryx Starts Phase 1 Trial of BTX-9341 for HR+/HER2- Breast Cancer

SAN DIEGO, July 17, 2024 – Biotheryx, Inc., a biopharmaceutical company focused on the discovery and development of innovative protein degraders for cancer and inflammatory diseases, has announced the initiation of its Phase 1 clinical trial for BTX-9341. This investigational oral drug targets cyclin-dependent kinases 4 and 6 (CDK4/6) and will be tested both as a monotherapy and in combination with fulvestrant for patients with advanced or metastatic hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer who have previously undergone CDK4/6 inhibitor therapy.

Leah Fung, Ph.D., CEO of Biotheryx, conveyed her optimism about the trial, highlighting the potential of BTX-9341 to address an unmet medical need in HR+/HER2- breast cancer patients who have received prior CDK4/6 inhibitor treatments. Fung emphasized the significance of dosing the first patient, marking a major milestone for the company and the scientific community involved in this endeavor.

This Phase 1 clinical trial will initially focus on dose escalation of BTX-9341 as a standalone treatment. Subsequently, it will explore the combination of BTX-9341 with fulvestrant, culminating in a dose expansion phase for the combination treatment. The trial aims to evaluate the safety, tolerability, pharmacokinetic, and pharmacodynamic properties of BTX-9341 both as a monotherapy and in combination with fulvestrant. Once the optimal Phase 2 dose for the combination is established, the trial will formally assess its efficacy in an expanded patient cohort.

Dr. Amita Patnaik, Co-Founder and Co-Director of Clinical Research at The START Center for Cancer Research, expressed enthusiasm about the advancement of BTX-9341 into clinical evaluation. She described BTX-9341 as a groundbreaking, potent, and selective degrader of CDK4/6 with the potential to revolutionize the treatment landscape for patients with advanced or metastatic HR+/HER2- breast cancer, particularly those previously treated with CDK4/6 inhibitors. Patnaik noted that this milestone aligns with START's mission to expedite drug development and provide early access to innovative anticancer therapies.

Preclinical studies have shown that BTX-9341, when administered orally, effectively degrades CDK4/6 in vivo and demonstrates enhanced anti-tumor activity as a monotherapy in comparison to current standard treatments. Additionally, BTX-9341 has exhibited synergistic effects with selective estrogen receptor degraders such as fulvestrant, elacestrant, and camizestrant in models resistant and naïve to CDK4/6 inhibitors.

BTX-9341 stands out as a first-in-class oral degrader of CDK4/6, crucial targets in various cancers and validated in HR+/HER2- breast cancer. In preclinical models, BTX-9341 has shown superior effectiveness compared to CDK4/6 inhibitors through potent and selective degradation of CDK4 and CDK6, inhibition of Cyclin E and CDK2 transcription, cell cycle arrest, and superior efficacy in breast cancer xenografts. Unlike CDK4/6 inhibitors, BTX-9341 can overcome resistance mechanisms in second-line HR+/HER2- breast cancer.

Biotheryx, Inc. is a clinical-stage biopharmaceutical company dedicated to discovering and developing a range of innovative protein degraders, including bifunctional degraders and molecular glues, targeting validated proteins in cancer and inflammatory diseases. Leveraging their expertise in Cereblon binding, the company has developed the proprietary PRODEGY platform. Biotheryx's pipeline includes BTX-9341, a bifunctional degrader of CDK4/6, which has entered a Phase 1 clinical trial, as well as BTX-10908, a degrader of SOS1 for pan-KRAS mutant cancers, and PDE4 degraders for inflammatory diseases.